The system (hereinafter referred to as a fuel cell system) that includes polymer electrolyte fuel cell (hereinafter referred simply to as a fuel cell) and mechanisms for feeding a fuel etc. into it comprises the type in which hydrogen is fed to the fuel cell and the type (refer to, e.g., Patent document 2, 4, 5) in which hydrogen generated by reforming town gas, methanol etc. is fed to the fuel cell, as well known. The fuel cell system (refer to, e.g., Patent document 1, 3) in which methanol, ethanol or the like is fed to the fuel cell directly (without being reformed) is also known.
The fuel cell system in which a liquid fuel (methanol etc.) is directly fed to the fuel cell has advantages in that a reformer is not required and the liquid, which can be stored and transported more easily than hydrogen, can be used as the fuel.
However, when the liquid fuel is directly fed to the fuel cell, a phenomenon by which the liquid fuel diffuses into the cathode through the electrolyte film occurs. The phenomenon is normally termed a crossover. The occurrence of the crossover causes useless consumption of the fuel. Further, the oxidation of the fuel that is crossovered into the cathode fuel causes lowering of the output of the fuel cell. Hence, the efforts to develop the electrolyte films in which the crossover does not occur and the catalysts (refer to, e.g., Patent document 1) that does not oxidize the crossovered fuel are made.    [Patent document 1] Japanese Patent Laid-Open Publication No. 2008-016344    [Patent document 2] Japanese Patent Laid-Open Publication No. 2006-511923    [Patent document 3] Japanese Patent Laid-Open Publication No. 2008-097838    [Patent document 4] Japanese Patent Laid-Open Publication No. 2001-250573    [Patent document 5] Japanese Patent Laid-Open Publication No. 2003-017096